This is a plain triple neck ring miniature decanter circa 1800. It is 7.5 inches high including the stopper.

I bought this expecting the stopper to be a wrong'un, but when I looked at it closely it appears to be the original. It is period, the glass colour matches, it fits perfectly, and it looks like it has 200 years of wearing into the peg hole. I can only think this is so small (you can only get one modern glass of wine in it), that they didn't make a bullseye for it. There is something to be learned every day.